Open-loop voltage regulation and drift compensation for digitally controlled oscillator (dco)

ABSTRACT

Embodiments include apparatuses, methods, and systems for open-loop voltage regulation and drift compensation for a digitally controlled oscillator (DCO). In embodiments, a communication circuit may include a DCO, an open-loop voltage regulator, and a calibration circuit. The open-loop voltage regulator may receive a calibration voltage and may generate a regulated voltage. The regulated voltage may be passed to the DCO. During a calibration mode, the calibration circuit may compare the regulated voltage to a reference voltage and adjust the calibration voltage based on the comparison to provide the regulated voltage with a target value. During a monitoring mode, the calibration circuit may receive a tuning code that is used to tune the DCO and further adjust the calibration voltage based on a value of the tuning code.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/498,728, filed Sep. 26, 2014, entitled “OPEN-LOOP VOLTAGEREGULATION AND DRIFT COMPENSATION FOR DIGITALLY CONTROLLED OSCILLATOR(DCO),” the entire disclosure of which is hereby incorporated byreference in its entirety.

FIELD

Embodiments of the present invention relate generally to the technicalfield of electronic circuits, and more particularly to open-loop voltageregulation and drift compensation for digitally controlled oscillators(DCOs).

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure. Unless otherwise indicated herein, the approaches describedin this section are not prior art to the claims in the presentdisclosure and are not admitted to be prior art by inclusion in thissection.

Many digitally controlled oscillators (DCOs) include a ring oscillator.However, the ring oscillator typically includes high sensitivity tosupply noise (e.g., the frequency of the oscillator varies significantlywith a change in supply voltage) and high intrinsic jitter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be readily understood by the following detaileddescription in conjunction with the accompanying drawings. To facilitatethis description, like reference numerals designate like structuralelements. Embodiments are illustrated by way of example and not by wayof limitation in the figures of the accompanying drawings.

FIG. 1 schematically illustrates a circuit including a digitallycontrolled oscillator (DCO), an open-loop voltage regulator, and acalibration circuit in accordance with various embodiments.

FIG. 2 illustrates an example DCO in accordance with variousembodiments.

FIG. 3 illustrates an example method in accordance with variousembodiments.

FIG. 4 illustrates an example system configured to employ theapparatuses and methods described herein, in accordance with variousembodiments.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof wherein like numeralsdesignate like parts throughout, and in which is shown by way ofillustration embodiments that may be practiced. It is to be understoodthat other embodiments may be utilized and structural or logical changesmay be made without departing from the scope of the present disclosure.Therefore, the following detailed description is not to be taken in alimiting sense, and the scope of embodiments is defined by the appendedclaims and their equivalents.

Various operations may be described as multiple discrete actions oroperations in turn, in a manner that is most helpful in understandingthe claimed subject matter. However, the order of description should notbe construed as to imply that these operations are necessarily orderdependent. In particular, these operations may not be performed in theorder of presentation. Operations described may be performed in adifferent order than the described embodiment. Various additionaloperations may be performed and/or described operations may be omittedin additional embodiments.

For the purposes of the present disclosure, the phrases “A and/or B” and“A or B” mean (A), (B), or (A and B). For the purposes of the presentdisclosure, the phrase “A, B, and/or C” means (A), (B), (C), (A and B),(A and C), (B and C), or (A, B, and C).

The description may use the phrases “in an embodiment,” or “inembodiments,” which may each refer to one or more of the same ordifferent embodiments. Furthermore, the terms “comprising,” “including,”“having,” and the like, as used with respect to embodiments of thepresent disclosure, are synonymous.

As used herein, the term “circuitry” may refer to, be part of, orinclude an Application Specific Integrated Circuit (ASIC), an electroniccircuit, a processor (shared, dedicated, or group), and/or memory(shared, dedicated, or group) that execute one or more software orfirmware programs, a combinational logic circuit, and/or other suitablehardware components that provide the described functionality. As usedherein, “computer-implemented method” may refer to any method executedby one or more processors, a computer system having one or moreprocessors, a mobile device such as a smartphone (which may include oneor more processors), a tablet, a laptop computer, a set-top box, agaming console, and so forth.

FIG. 1 schematically illustrates a circuit 100 in accordance withvarious embodiments. The circuit 100 may include a digitally controlledoscillator (DCO) 102 to generate an output signal at an output terminal103. The circuit 100 may further include an open-loop voltage regulator104 coupled to the DCO 102. The open-loop voltage regulator 104 may becoupled to a supply rail 106 to receive a supply voltage (Vcc). Theopen-loop voltage regulator 104 may be further coupled to a power inputterminal 108 of the DCO 102 to provide a regulated voltage, Vreg, to theDCO 102. The regulated voltage, Vreg, may be used by the DCO 102 as asupply voltage.

In various embodiments, the DCO 102 may receive a coarse tuning code ata coarse tuning input 109 of the DCO 102 and may receive a fine tuningcode at a fine tuning input 111 of the DCO 102. The coarse tuning codeand fine tuning code may be digital codes (e.g., including a pluralityof bits). The frequency of the output signal generated by the DCO 102may be adjusted by adjusting the coarse tuning code and/or the finetuning code. The coarse tuning code may be used to make largeradjustments in the frequency of the output signal than the fine tuningcode. In some embodiments, the coarse tuning code and the fine tuningcode may be provided by a tuning circuit 115. The tuning circuit 115 mayadjust the coarse tuning code and/or fine tuning code so that the outputfrequency has a desired frequency (e.g., using a feedback loop). In someembodiments, the tuning circuit 115 may adjust the coarse tuning codeand/or fine tuning code using a proportional, integral, derivativecontroller (e.g., using proportional, integral, and derivative values).

In various embodiments, the circuit 100 may further include acalibration circuit 110 coupled to the open-loop voltage regulator 104.During a calibration mode of the circuit 100, the calibration circuit110 may adjust the value of a calibration voltage, Vcal, received by theopen-loop voltage regulator 104. In various embodiments, the calibrationvoltage, Vcal, may be adjusted to provide the regulated voltage, Vreg,with a target value (e.g., a pre-defined target value). Aftercalibration, the circuit 100 and/or DCO 102 may enter a normal operatingmode. Accordingly, the calibration of the calibration voltage, Vcal, maycompensate for process variation and/or other factors in the open-loopvoltage regulator 104.

In some embodiments, during the normal operating mode, the calibrationcircuit 110 may further adjust the calibration voltage, Vcal, tocompensate for drift in one or more tuning codes used to tune the DCO102 to generate the output signal with the desired frequency. Forexample, the calibration circuit 110 may receive a tuning code (e.g.,the fine tuning code) that is used to adjust the frequency of the outputsignal generated by the DCO 102, and the calibration circuit 110 mayadjust the calibration voltage Vcal so that the tuning code remainswithin a pre-determined range of code values. Monitoring andcompensating for the drift in the tuning code may allow a DCO with alower tuning range (e.g., a lower number of bits for the tuning code) tobe used than in circuits that do not monitor and compensate for thedrift in the tuning code.

FIG. 2 illustrates an example DCO 200 that may be included in the DCO102 of FIG. 1 in some embodiments. The DCO 200 may include a pluralityof inverters 202 a-c coupled in series with one another (e.g., with theoutput of inverter 202 a coupled to the input of inverter 202 b, etc.).The inverters 202 a-c may form a feedback loop, with the output ofinverter 202 c being coupled to the input of inverter 202 a. Theinverters 202 a-c may be coupled to a power input terminal 204 toreceive a regulated supply voltage (e.g., the regulated voltage, Vreg,of FIG. 1). The inverters 202 a-c may be further coupled to a coarsetuning input 206 to receive a coarse tuning code. The coarse tuning codemay be used to adjust the gain of the inverters 202 a-c. In variousembodiments, the DCO 200 may further include a plurality of capacitorbanks 208 a-c coupled between respective nodes between pairs of theinverters 202 a-c. The capacitor banks 208 a-c may be coupled to a finetuning input 210 to receive a fine tuning code. The fine tuning code maybe used to adjust the capacitance provided by the capacitor banks 208a-c. Other embodiments may include another type of DCO and/or use othertuning mechanisms to tune the frequency of the DCO.

In various embodiments, the DCO 200 may generate an output signal at anoutput terminal 212. A frequency of the output signal may be tuned byadjusting the coarse tuning code and/or the fine tuning code. However,the DCO 200 may have a high sensitivity to variation in the regulatedvoltage Vreg. Additionally, the frequency of the output signal generatedby the DCO 200 may vary across process, voltage, and/or temperature(PVT) conditions. In various embodiments, the open-loop voltageregulator 104 of the circuit 100 may provide the regulated voltage Vregwith low-noise. Additionally, the calibration circuit 110 of circuit 100may adjust the value of the regulated voltage Vreg to compensate for PVTvariation in the voltage regulator 104 and/or DCO 200.

Referring again to FIG. 1, the open-loop voltage regulator 104 mayinclude one or more regulator stages 112 a-b. The individual regulatorstages 112 a-b may include a low-pass filter 114 a-b coupled to atransistor 116 a-b. The filter 114 a-b may be coupled to a gate terminalof the respective transistor 116 a-b. Accordingly, the filter 114 a-bmay filter the voltage that is passed to the gate terminal of therespective transistor 116 a-b.

In some embodiments, the low-pass filters 114 a-b may beresistance-capacitance (RC) filters including one or more resistors 118a-b and one or more capacitors 120 a-b. Although the filters 114 a-b areshown in FIG. 1 to be first-order filters including a single resistor118 a-b and a single capacitor 120 a-b, other embodiments may be second-or higher-order filters including a plurality of resistors and/orcapacitors. The resistors 118 a may be coupled between a gate terminalof the transistor 116 a and node 122 that receives the calibrationvoltage Vcal. The capacitor 120 a may be coupled in shunt with the gateterminal of the transistor 116. The filters 114 a-b may filter outhigh-frequency noise in the calibration voltage Vcal to provide theregulated voltage Vreg with low noise.

The open-loop voltage regulator 104 may not filter out low frequencynoise. However, any low-frequency noise may be suppressed by aphase-locked loop (PLL) and/or clock-and-data recovery circuit (CDR).

In embodiments in which the open-loop voltage regulator 104 includesmultiple regulator stages 112 a-b, the regulator stages 112 a-b may becascaded, with the transistors 116 a-b coupled in series between thesupply rail 106 and the power input terminal 108 of the DCO 102. Inother embodiments, the open-loop voltage regulator may include only asingle regulator stage (e.g., may include regulator stage 112 a but notregulator stage 112 b). For example, the open-loop voltage regulator 104may include a plurality of regulator stages 112 a-b in embodiments inwhich the supply voltage Vcc is higher. In one non-limiting example, asingle regulator stage 112 a may be used when the supply voltage Vcc isabout 1.24-1.35 Volts, and two regulator stages 112 a-b may be used whenthe supply voltage Vcc is about 1.8 Volts or higher. In yet otherembodiments, the open-loop voltage regulator 104 may include more thantwo regulator stages 112 a-b.

In various embodiments, the open-loop voltage regulator 104 may generatethe regulated voltage Vreg with low-noise. Additionally, the open-loopvoltage regulator 104 may consume only a small amount (e.g., negligibleamount) of current. However, the open-loop voltage regulator 104 may besusceptible to variation across PVT conditions. Accordingly, thecalibration circuit 110 may be included in the circuit 100 to compensatefor variation in PVT conditions, as described herein.

In various embodiments, the calibration circuit 110 may include acomparator 124, a potentiometer 126 (e.g., a digital potentiometer),and/or a control circuit 128. In various embodiments, the potentiometer126 may be coupled to the open-loop voltage regulator 104 (e.g., withthe variable impedance terminal of the potentiometer 126 coupled to theinput of the low-pass filter 114 a of the regulator stage 112 a).Accordingly, the calibration circuit 110 may adjust the impedance of thepotentiometer 126 to adjust the value of the calibration voltage, Vcal.

In various embodiments, a first input of the comparator 124 may becoupled to the power input terminal 108 to receive the regulated voltageVreg. A second input of the comparator 124 may receive a referencevoltage Vref. The reference voltage Vref may correspond to the targetvalue of the regulated voltage Vreg. In some embodiments, the firstinput of the comparator 124 may receive the regulated voltage Vreg via avoltage divider 130. The voltage divider 130 may scale the regulatedvoltage Vreg so that the scaled value of the regulated voltage isapproximately equal to the reference voltage Vref. An output of thecomparator 124 may be coupled to the control circuit 128. The controlcircuit 128 may be further coupled to the potentiometer 126 to controlthe impedance of the potentiometer 126.

During a calibration process (performed when the circuit 100 is in thecalibration mode), the comparator may compare the regulated voltage Vregto the reference voltage Vref and pass the results of the comparison tothe control circuit 128. The control circuit 128 may adjust theimpedance of the potentiometer 126, based on the comparison by thecomparator 124, to adjust the calibration voltage Vcal provided to theopen-loop voltage regulator 104 until the regulated voltage Vregreceived by the comparator 124 is approximately equal to the referencevoltage Vref. Accordingly, the first portion of the calibration processmay calibrate the regulated voltage Vreg to have the target value.Calibration of the regulated voltage Vreg to the target value maycompensate for process variation in the open-loop voltage regulator 104(e.g., in the transistors 116 a-b of the open-loop voltage regulator104). In some embodiments, the target value may cause the DCO 102 to beapproximately in the middle of its tuning range.

After the regulated voltage, Vreg, has been calibrated to the targetvalue, the DCO 102 may be tuned to generate the output signal with thedesired frequency. The DCO 102 may first be coarsely tuned using thecoarse tuning code, and then finely tuned using the fine tuning code.After completion of the calibration process, the circuit may transitionfrom the calibration mode to a normal operating mode.

In various embodiments, the calibration circuit 110 may enter amonitoring mode during normal operation of the DCO 102. During themonitoring mode, the control circuit 128 may monitor for drift in atuning code (e.g., the fine tuning code) of the DCO 102. For example,the control circuit 128 may receive the fine tuning code (e.g., the finetuning code) that is used to tune the output frequency generated by theDCO 102. The control circuit 128 may determine if the tuning code isoutside a pre-determined range of tuning codes. The pre-determined rangeof tuning codes may be defined by an upper threshold and a lowerthreshold. The upper threshold may be less than a maximum possible valueof the tuning code, and the lower threshold may be greater than aminimum possible value of the tuning code. Accordingly, thepre-determined range of tuning codes may include less than all possiblevalues for the tuning code.

If the control circuit 128 determines that the tuning code is outsidethe pre-determined range of tuning codes (e.g., the tuning code isgreater than the upper threshold or less than the lower threshold), thenthe control circuit 128 may adjust the value of the calibration voltageVcal (e.g., by adjusting the impedance of the potentiometer 126) so thatthe tuning code is inside the pre-determined range of tuning codes(e.g., after the tuning circuit 115 adjusts the tuning code tocompensate for the change in the value of the regulated supply voltageVreg caused by the change in the calibration voltage Vcal). For example,the control circuit 128 may adjust the value of the calibration voltageVcal so that the tuning code is substantially in the middle of thepre-determined range of tuning codes.

Accordingly, the monitoring of the tuning code by the control circuit128 may compensate for drift in the DCO 102 (e.g., due to temperaturechanges, aging, or other factors).

FIG. 3 illustrates a method 300 in accordance with various embodiments.The method 300 may be performed by a calibration circuit (e.g.,calibration circuit 110) that is coupled to an open-loop voltageregulator (e.g., open-loop voltage regulator 104) and a DCO (e.g., DCO102). In some embodiments, the calibration circuit may include one ormore non-transitory computer-readable media having instructions, storedthereon, that when executed case the calibration circuit to perform themethod 300.

At block 302, the method 300 may include comparing, by the calibrationcircuit, a regulated voltage provided to the DCO with a referencevoltage, wherein the regulated voltage is provided to the DCO by anopen-loop voltage regulator.

At block 304, the method 300 may include adjusting, based on thecomparison, a calibration voltage provided to the open-loop voltageregulator to provide the regulated voltage with a target value.

At block 306, the method 300 may include monitoring drift of a tuningcode that is used to tune the DCO. For example, the DCO may receive acoarse tuning code and a fine tuning code, and block 306 may includemonitoring the fine tuning code.

At block 308, the method 300 may include further adjusting thecalibration voltage based on the monitored drift.

In some embodiments, the monitoring the drift at block 306 of the method300 may include receiving the tuning code and determining if the tuningcode is outside a pre-determined range of tuning codes. Additionally,the further adjusting the calibration voltage at block 308 may include,if the tuning code is outside the pre-determined range of tuning codes,adjusting the calibration voltage so that the tuning code is inside thepre-determined range of tuning codes.

FIG. 4 illustrates an example computing device 400 that may employ theapparatuses and/or methods described herein (e.g., circuit 100, DCO 200,method 300), in accordance with various embodiments. As shown, computingdevice 400 may include a number of components, such as one or moreprocessor(s) 404 (one shown) and at least one communication chip 406. Invarious embodiments, the one or more processor(s) 404 each may includeone or more processor cores. In various embodiments, the at least onecommunication chip 406 may be physically and electrically coupled to theone or more processor(s) 404. In further implementations, thecommunication chip 406 may be part of the one or more processor(s) 404.In various embodiments, computing device 400 may include printed circuitboard (PCB) 402. For these embodiments, the one or more processor(s) 404and communication chip 406 may be disposed thereon. In alternateembodiments, the various components may be coupled without theemployment of PCB 402.

Depending on its applications, computing device 400 may include othercomponents that may or may not be physically and electrically coupled tothe PCB 402. These other components include, but are not limited to,memory controller 405, volatile memory (e.g., dynamic random accessmemory (DRAM) 408), non-volatile memory such as read only memory (ROM)410, flash memory 412, storage device 411 (e.g., a hard-disk drive(HDD)), an I/O controller 414, a digital signal processor (not shown), acrypto processor (not shown), a graphics processor 416, one or moreantenna 418, a display (not shown), a touch screen display 420, a touchscreen controller 422, a battery 424, an audio codec (not shown), avideo codec (not shown), a global positioning system (GPS) device 428, acompass 430, an accelerometer (not shown), a gyroscope (not shown), aspeaker 432, a camera 434, and a mass storage device (such as hard diskdrive, a solid state drive, compact disk (CD), digital versatile disk(DVD)) (not shown), and so forth. In various embodiments, the processor404 may be integrated on the same die with other components to form aSystem on Chip (SoC).

In some embodiments, the one or more processor(s) 404, flash memory 412,and/or storage device 411 may include associated firmware (not shown)storing programming instructions configured to enable computing device400, in response to execution of the programming instructions by one ormore processor(s) 404, to practice all or selected aspects of themethods described herein (e.g., method 300). In various embodiments,these aspects may additionally or alternatively be implemented usinghardware separate from the one or more processor(s) 404, flash memory412, or storage device 411.

In various embodiments, one or more components of the computing device400 may include the circuit 100 and/or DCO 200 described herein. Forexample, the circuit 100 and/or DCO 200 may be included in I/Ocontroller 414, processor 404, memory controller 405, and/or anothercomponent of computing device 400. In some embodiments, the circuit 100and/or DCO 200 may be used in a High-Speed Serial Link application(e.g., to generate a clock signal and/or other oscillating signal).

The communication chips 406 may enable wired and/or wirelesscommunications for the transfer of data to and from the computing device400. The term “wireless” and its derivatives may be used to describecircuits, devices, systems, methods, techniques, communicationschannels, etc., that may communicate data through the use of modulatedelectromagnetic radiation through a non-solid medium. The term does notimply that the associated devices do not contain any wires, although insome embodiments they might not. The communication chip 406 mayimplement any of a number of wireless standards or protocols, includingbut not limited to IEEE 702.20, Long Term Evolution (LTE), LTE Advanced(LTE-A), General Packet Radio Service (GPRS), Evolution Data Optimized(Ev-DO), Evolved High Speed Packet Access (HSPA+), Evolved High SpeedDownlink Packet Access (HSDPA+), Evolved High Speed Uplink Packet Access(HSUPA+), Global System for Mobile Communications (GSM), Enhanced Datarates for GSM Evolution (EDGE), Code Division Multiple Access (CDMA),Time Division Multiple Access (TDMA), Digital Enhanced CordlessTelecommunications (DECT), Worldwide Interoperability for MicrowaveAccess (WiMAX), Bluetooth, derivatives thereof, as well as any otherwireless protocols that are designated as 3G, 4G, 5G, and beyond. Thecomputing device 400 may include a plurality of communication chips 406.For instance, a first communication chip 406 may be dedicated to shorterrange wireless communications such as Wi-Fi and Bluetooth, and a secondcommunication chip 406 may be dedicated to longer range wirelesscommunications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, andothers.

In various implementations, the computing device 400 may be a laptop, anetbook, a notebook, an ultrabook, a smartphone, a computing tablet, apersonal digital assistant (PDA), an ultra-mobile PC, a mobile phone, adesktop computer, a server, a printer, a scanner, a monitor, a set-topbox, an entertainment control unit (e.g., a gaming console or automotiveentertainment unit), a digital camera, an appliance, a portable musicplayer, or a digital video recorder. In further implementations, thecomputing device 400 may be any other electronic device that processesdata.

Some non-limiting Examples are provided below.

Example 1 is a voltage regulation circuit comprising: a supply rail toreceive a supply voltage; an open-loop voltage regulator coupled to thesupply rail and including a transistor, the open-loop voltage regulatorto provide a regulated voltage to a digital-controlled oscillator (DCO);and a calibration circuit coupled to the open-loop voltage regulator,the calibration circuit to, during a calibration mode of the circuit,adjust a calibration voltage provided to the open-loop voltage regulatorto provide the regulated voltage with a target value.

Example 2 is the circuit of Example 1, further comprising the DCOcoupled to the open-loop voltage regulator.

Example 3 is the circuit of Example 1, wherein the calibration circuitincludes: a potentiometer coupled to the open-loop voltage regulator; acomparator to compare the regulated voltage to a reference voltage; anda control circuit coupled to the potentiometer and the comparator, thecontrol circuit to adjust an impedance of the potentiometer, based onthe comparison by the comparator, to adjust the calibration voltageprovided to the open-loop voltage regulator.

Example 4 is the circuit of Example 1, wherein a drain terminal of thetransistor is coupled to the DCO to provide the regulated voltage,wherein the open-loop voltage regulator further includes a low-passresistance-capacitance (RC) filter coupled to a gate terminal of thetransistor.

Example 5 is the circuit of Example 4, wherein the transistor, theresistor, and the capacitor are included in a first stage of theopen-loop voltage regulator, and wherein the open-loop voltage regulatorfurther includes a second stage that has a transistor coupled betweenthe transistor of the first stage and the supply rail.

Example 6 is the circuit of any one of Examples 1 to 5, wherein thecalibration circuit is further to: receive a digital tuning code that isused to tune an output frequency of the DCO; determine if the tuningcode is outside a pre-determined range of tuning codes; and if thetuning code is outside the pre-determined range of tuning codes, adjustthe calibration voltage so that the tuning code is inside thepre-determined range of tuning codes.

Example 7 is the circuit of Example 6, wherein the calibration circuitis to determine if the tuning code is outside the pre-determined rangeof tuning codes and to adjust the calibration voltage so that the tuningcode is inside the pre-determined range of tuning codes during normaloperation of the DCO and after adjusting the calibration voltageprovided to the open-loop voltage regulator to provide the regulatedvoltage with the target value during the calibration mode of the DCO.

Example 8 is the circuit of Example 6, wherein the tuning code is a finetuning code.

Example 9 is the circuit of Example 6, wherein the pre-determined rangeof tuning codes includes less than all possible values for the tuningcode.

Example 10 is a method for providing a regulated voltage to a digitallycontrolled oscillator (DCO), the method comprising: comparing, by acalibration circuit, a regulated voltage with a reference voltage,wherein the regulated voltage is provided to a DCO by an open-loopvoltage regulator; adjusting, based on the comparison, a calibrationvoltage provided to the open-loop voltage regulator to provide theregulated voltage with a target value; monitoring drift of a tuning codethat is used to tune the DCO; and further adjusting the calibrationvoltage based on the monitored drift.

Example 11 is the method of Example 10, wherein the monitoring the driftincludes: receiving the tuning code; and determining if the tuning codeis outside a pre-determined range of tuning codes; and wherein thefurther adjusting the calibration voltage based on the monitored driftincludes, if the tuning code is outside the pre-determined range oftuning codes, adjusting the calibration voltage so that the tuning codeis inside the pre-determined range of tuning codes.

Example 12 is the method of Example 10, wherein the adjusting thecalibration voltage is performed by controlling an impedance of adigital potentiometer coupled to the open-loop voltage regulator.

Example 13 is the method of Example 10, wherein the comparing theregulated voltage with the reference voltage and the adjusting, based onthe comparison, the calibration voltage are performed during acalibration mode of the DCO, and wherein the monitoring the drift of thetuning code and the further adjusting the calibration voltage based onthe monitored drift are performed during a normal operating mode of theDCO after the calibration mode.

Example 14 is the method of any one of Examples 10 to 13, wherein thetuning code is a fine tuning code, and wherein the DCO is further toreceive a coarse tuning code.

Example 15 is a computing system comprising: a display; a processorcoupled to the display; and a communication circuit coupled to theprocessor. The communication circuit includes: a digitally controlledoscillator (DCO); an open-loop voltage regulator to receive acalibration voltage and to provide a regulated voltage to the DCO basedon the calibration voltage; and a calibration circuit coupled to theopen-loop voltage regulator, the calibration circuit to: during acalibration mode, compare the regulated voltage to a reference voltageand adjust the calibration voltage based on the comparison; and during amonitoring mode, receive a tuning code that is used to tune the DCO andfurther adjust the calibration voltage based on a value of the tuningcode.

Example 16 is the system of Example 15, wherein the calibration circuitincludes: a potentiometer coupled to the open-loop voltage regulator; acomparator to compare the regulated voltage to a reference voltage; anda control circuit coupled to the potentiometer and the comparator, thecontrol circuit to adjust an impedance of the potentiometer, based onthe comparison by the comparator, to adjust the calibration voltageprovided to the open-loop voltage regulator.

Example 17 is the system of Example 15, wherein a drain terminal of thetransistor is coupled to the DCO to provide the regulated voltage,wherein the open-loop voltage regulator further includes a low-passfilter coupled to a gate terminal of the transistor.

Example 18 is the system of Example 17, wherein the transistor, theresistor, and the capacitor are included in a first stage of theopen-loop voltage regulator, and wherein the open-loop voltage regulatorfurther includes a second stage that has a transistor coupled betweenthe transistor of the first stage and a supply rail.

Example 19 is the system of Example 15, wherein, to further adjust thecalibration voltage based on the value of the tuning code, thecalibration circuit is to: determine if the value of the tuning code isoutside a pre-determined range of values; and if the value of the tuningcode is outside the pre-determined range of values, adjust thecalibration voltage so that the value of the tuning code is inside thepre-determined range of tuning codes.

Example 20 is the system of any one of Examples 15 to 19, wherein thecalibration circuit is to enter the calibration mode upon power up ofthe DCO, and wherein the calibration circuit is to be in the monitoringmode during normal operation of the DCO.

Example 21 is the system of Example 15, wherein the tuning code is afine tuning code, and wherein the DCO is to receive the fine tuning codeand a coarse tuning code.

Although certain embodiments have been illustrated and described hereinfor purposes of description, this application is intended to cover anyadaptations or variations of the embodiments discussed herein.Therefore, it is manifestly intended that embodiments described hereinbe limited only by the claims.

Where the disclosure recites “a” or “a first” element or the equivalentthereof, such disclosure includes one or more such elements, neitherrequiring nor excluding two or more such elements. Further, ordinalindicators (e.g., first, second, or third) for identified elements areused to distinguish between the elements, and do not indicate or imply arequired or limited number of such elements, nor do they indicate aparticular position or order of such elements unless otherwisespecifically stated.

What is claimed is:
 1. A circuit comprising: a digital-controlledoscillator (DCO); an open-loop voltage regulator coupled to the DCO, theopen-loop voltage regulator to provide a regulated voltage to thedigital-controlled oscillator (DCO); a calibration circuit coupled tothe open-loop voltage regulator, the calibration circuit to: receive adigital tuning code that is used to tune an output frequency of the DCO;determine if the tuning code is outside a pre-determined range of tuningcodes; and if the tuning code is outside the pre-determined range oftuning codes, adjust the calibration voltage so that the tuning code isinside the pre-determined range of tuning codes.
 2. The circuit of claim1, wherein the calibration circuit is further to, during a calibrationmode of the circuit, adjust a calibration voltage provided to theopen-loop voltage regulator to provide the regulated voltage with atarget value.
 3. The circuit of claim 2, wherein the calibration circuitincludes: a potentiometer coupled to the open-loop voltage regulator; acomparator to compare the regulated voltage to a reference voltage; anda control circuit coupled to the potentiometer and the comparator, thecontrol circuit to adjust an impedance of the potentiometer, based onthe comparison by the comparator, to adjust the calibration voltageprovided to the open-loop voltage regulator.
 4. The circuit of claim 2,wherein the open-loop voltage regulator includes: a transistor having adrain terminal coupled to the DCO to provide the regulated voltage; anda low-pass resistance-capacitance (RC) filter coupled to a gate terminalof the transistor.
 5. The circuit of claim 4, wherein the transistor andthe low-pass RC filter are included in a first stage of the open-loopvoltage regulator, and wherein the open-loop voltage regulator furtherincludes a second stage that has a transistor coupled between thetransistor of the first stage and the supply rail.
 6. The circuit ofclaim 1, wherein the calibration circuit is to determine if the tuningcode is outside the pre-determined range of tuning codes and to adjustthe calibration voltage so that the tuning code is inside thepre-determined range of tuning codes during normal operation of the DCOand after adjusting the calibration voltage provided to the open-loopvoltage regulator to provide the regulated voltage with the target valueduring the calibration mode of the DCO.
 7. The circuit of claim 1,wherein the tuning code is a fine tuning code.
 8. The circuit of claim1, wherein the pre-determined range of tuning codes includes less thanall possible values for the tuning code.
 9. An apparatus comprising:means for comparing a regulated voltage with a reference voltage,wherein the regulated voltage is provided to a digitally controlledoscillator (DCO) by an open-loop voltage regulator; means for adjusting,based on the comparison, a calibration voltage provided to the open-loopvoltage regulator to provide the regulated voltage with a target value;means for monitoring drift of a tuning code that is used to tune theDCO; and means for further adjusting the calibration voltage based onthe monitored drift to maintain a value of the tuning code within apre-determined range.
 10. The apparatus of claim 9, wherein the meansfor monitoring the drift includes means for determining if the tuningcode is outside the pre-determined range of tuning codes; and whereinthe means for further adjusting the calibration voltage based on themonitored drift includes means for, if the tuning code is outside thepre-determined range of tuning codes, adjusting the calibration voltageso that the tuning code is inside the pre-determined range of tuningcodes.
 11. The apparatus of claim 9, wherein the means for adjusting thecalibration voltage includes means for controlling an impedance of adigital potentiometer coupled to the open-loop voltage regulator. 12.The apparatus of claim 9, wherein the comparing the regulated voltagewith the reference voltage and the adjusting, based on the comparison,the calibration voltage are to be performed during a calibration mode ofthe DCO, and wherein the monitoring the drift of the tuning code and thefurther adjusting the calibration voltage based on the monitored driftare to be performed during a normal operating mode of the DCO after thecalibration mode.
 13. The apparatus of claim 9, wherein the tuning codeis a fine tuning code, and wherein the apparatus further includes meansfor receiving a coarse tuning code for the DCO.
 14. A system comprising:a processor; and a communication circuit coupled to the processor, thecommunication circuit including: a digitally controlled oscillator(DCO); an open-loop voltage regulator to receive a calibration voltageand to provide a regulated voltage to the DCO based on the calibrationvoltage; and a calibration circuit coupled to the open-loop voltageregulator, the calibration circuit to: during a calibration mode,compare the regulated voltage to a reference voltage and adjust thecalibration voltage, based on the comparison, to provide the regulatedvoltage with a pre-determined target voltage value; and during amonitoring mode, receive a tuning code that is used to tune the DCO andfurther adjust the calibration voltage based on a value of the tuningcode.
 15. The system of claim 14, wherein the calibration circuitincludes: a potentiometer coupled to the open-loop voltage regulator; acomparator to compare the regulated voltage to a reference voltage; anda control circuit coupled to the potentiometer and the comparator, thecontrol circuit to adjust an impedance of the potentiometer, based onthe comparison by the comparator, to adjust the calibration voltageprovided to the open-loop voltage regulator.
 16. The system of claim 14,wherein the open-loop voltage regulator includes a transistor, wherein adrain terminal of the transistor is coupled to the DCO to provide theregulated voltage, and wherein the open-loop voltage regulator furtherincludes a low-pass filter coupled to a gate terminal of the transistor.17. The system of claim 16, wherein the transistor and the low-passfilter are included in a first stage of the open-loop voltage regulator,and wherein the open-loop voltage regulator further includes a secondstage that has a transistor coupled between the transistor of the firststage and a supply rail.
 18. The system of claim 14, wherein, to furtheradjust the calibration voltage based on the value of the tuning code,the calibration circuit is to: determine if the value of the tuning codeis outside a pre-determined range of values; and if the value of thetuning code is outside the pre-determined range of values, adjust thecalibration voltage so that the value of the tuning code is inside thepre-determined range of tuning codes.
 19. The system of claim 14,wherein the calibration circuit is to enter the calibration mode uponpower up of the DCO, and wherein the calibration circuit is to be in themonitoring mode during normal operation of the DCO.
 20. The system ofclaim 14, wherein the tuning code is a fine tuning code, and wherein theDCO is to receive the fine tuning code and a coarse tuning code.
 21. Thesystem of claim 14, further comprising a display coupled to theprocessor.